Error correction methods that use soft information have been widely adopted to obtain the low levels of Uncorrectable Bit Error Rate (UBER) required for client and enterprise Solid State Drives (SSD's). Error correction methods that use soft information typically require testing sample flash memory devices in a lab to identify Log Likelihood Ratio (LLR) values that indicate the Bit Error Rate (BER) of the tested devices. The LLR's are then stored in tables in each SSD that are used by the memory controller for decoding reads of NAND flash memory chips.
The process of characterizing NAND flash memory chips is expensive and time consuming. In addition, the characteristics of NAND flash memory chips change during the lifetime of the NAND flash memory device, making accurate characterization difficult and requiring the storage of numerous LLR tables. Also, the storage space required for storing the LLR tables adds expense to the SSD.
Accordingly, there is a need for a method and apparatus that will allow for error correction using soft information that does not require lab testing of exemplary NAND flash memory chips and that will provide LLR values that accurately indicate the BER of the NAND flash memory chips.